RE: nRF52 timer as counter, Adafruit Feather

haakonsh — Wed, 17 Jun 2020 11:23:56 GMT

The TIMER, GPIOTE, and PPI peripherals are identical on the 832 and 840 so that's a reasonable assumption.

RE: nRF52 timer as counter, Adafruit Feather

arlenn — Wed, 17 Jun 2020 07:12:33 GMT

The above code has small problems, but I think the biggest problem was my misuse of the static variable. I think the compiler should have probably complained but it didn't. So it is working. Yay.

Below is the result. This is tested working on an Adafruit Feather nRF25832, but should probably work on an 840 as well?

#define FREQ_MEASURE_PIN 7u
#define PPI_CHANNEL 1u

void setup() {
  Serial.begin(115200);
  pinMode(LED_RED, OUTPUT);
  initCounter();
}

void loop() 
{  
  readCounter();
  digitalToggle(LED_RED);
  delay(1000);
}

void readCounter()
{
  static int counts;
  NRF_TIMER2->TASKS_CAPTURE[0] = 1;
  counts = NRF_TIMER2->CC[0];
  Serial.print("pulses: "); Serial.println(counts);
  //NRF_TIMER2->TASKS_CLEAR = 1;                  
  //NRF_TIMER2->TASKS_START = 1;
}

void initCounter()
{    
  NRF_P0->PIN_CNF[FREQ_MEASURE_PIN] = GPIO_PIN_CNF_DIR_Input << GPIO_PIN_CNF_DIR_Pos |
                                      GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos |
                                      GPIO_PIN_CNF_PULL_Pullup << GPIO_PIN_CNF_PULL_Pos |
                                      GPIO_PIN_CNF_SENSE_Low << GPIO_PIN_CNF_SENSE_Pos;

  NRF_PPI->CHEN |= 1 << PPI_CHANNEL;
  NRF_PPI->CH[PPI_CHANNEL].EEP = (uint32_t)&NRF_GPIOTE->EVENTS_IN[PPI_CHANNEL];
  NRF_PPI->CH[PPI_CHANNEL].TEP = (uint32_t)&NRF_TIMER2->TASKS_COUNT;

  NRF_GPIOTE->CONFIG[PPI_CHANNEL] = GPIOTE_CONFIG_MODE_Event << GPIOTE_CONFIG_MODE_Pos |
                                    FREQ_MEASURE_PIN << GPIOTE_CONFIG_PSEL_Pos |
                                    GPIOTE_CONFIG_POLARITY_HiToLo << GPIOTE_CONFIG_POLARITY_Pos; 

  NRF_TIMER2->TASKS_STOP = 1;   
  NRF_TIMER2->TASKS_CLEAR = 1;
  NRF_TIMER2->MODE = TIMER_MODE_MODE_LowPowerCounter << TIMER_MODE_MODE_Pos;
  NRF_TIMER2->BITMODE = TIMER_BITMODE_BITMODE_32Bit << TIMER_BITMODE_BITMODE_Pos;
  NRF_TIMER2->TASKS_START = 1;
}

RE: nRF52 timer as counter, Adafruit Feather

arlenn — Tue, 16 Jun 2020 16:17:06 GMT

Thanks for your help. I have actually tried it both ways. There were examples showing both, but it is good to know it is required. adding the & doesn't improve the situation in my case.

RE: nRF52 timer as counter, Adafruit Feather

Dmitry — Tue, 16 Jun 2020 08:28:24 GMT

Hi,

it seems the most common mistake when using PPI directly: missing & operator

NRF_PPI->CH[6].EEP = (uint32_t) &NRF_GPIOTE->EVENTS_IN[6];